Surge protection circuits are designed to protect electronic equipment from damage due to surge events that may cause large transient over voltage or current spike. Surge events may result from lightning strikes, switching impulses, electrical line noise, and other transients or abnormal conditions and malfunctions. For example, a lightning strike may cause a surge of 20 kV that can destroy equipment absent surge protection to prevent such destruction. Surge protection can block surges before they reach the electronic equipment by limiting the voltage, diverting the current through an alternate signal path, or both.
Examples of surge protectors include primary and secondary protection devices. Generally, a primary protection device is one that typically controls the electric power service entrance, operating as a main disconnect, and a secondary protection device can be connected upstream or downstream of the main disconnect. Surge protection devices may be constructed using fuses, inductors, clamping devices such as metal oxide varistors (MOVs), zener diodes, gas tubes, or various combinations of such devices as well as others.
Different systems may require different protection measures and possibly different types of surge protection mechanisms. Among such systems are wireless communication or wireless radio systems that can be configured as point-to-point, point-to-multipoint, and mesh networks consisting of multiple terminals. In some wireless communication systems each terminal or node includes digital and analog transceiver portions. The analog portion can include IF (intermediate frequency) and RF (radio frequency) content. With a split mount configuration, each node has an indoor unit (IDU) and an outdoor unit (ODU). The IDU connects to the network (e.g., Ethernet or Internet networks) and the ODU connected to an antenna. In this case, the IDU has a power supply and a modem or network interface and the ODU has an RF transceiver. The IDU can supply to the ODU DC power and modulated IF signals for transmission and it can receive from the ODU modulated IF signals received from the antenna. To this end, the IDU and ODU have an up-down connection between them using coaxial cable that can carry both power and IF signals (i.e., DC and non-DC signals).
In split mount systems such as the aforementioned wireless radio systems, both the ODU and IDU may need protection from surge events. Under regulatory guidelines, the IDU typically requires primary surge protection, i.e., at the power service entrance and at a coaxial cable connection point. Under such guidelines, the surge protection of the ODU can be provided inside or outside the ODU housing and it can be primary or secondary. In the ODU, internal surge suppression circuits provide only secondary protection and external surge arrestors may be costly and require a separate housing. An external surge arrestor is typically sealed from the environment and needs to be properly grounded.
Failures may occur, however, even with protection mechanisms as described above. For example, in split mount systems the up-down cable connectors may admit surge energy to components inside the wireless radio system and represent a vulnerable point in such systems. Thus, when there is a failure the system manufacturer (e.g., ODU and IDU manufacturer) may be required to perform a warranty repair without necessarily knowing whether the failure is due to a surge event, an inappropriate installation or another cause. There is therefore also a need to detect and better determine the causes of such malfunctions in order to determine, for instance, who might be responsible for the repair.